Automotive fuel system designers have long recognized the need for ensuring a continuous flow of fuel to the vehicle's fuel metering system during vehicle operation. This is commonly accomplished by positioning the fuel pump intake at a low point in the fuel tank so as to be covered while fuel remains in the tank. When the fuel level in the tank is low, however, the intake may become uncovered due to fuel "slosh" within the tank. The "slosh" phenomenon occurs during sudden or sharp vehicle cornering when fuel "sloshes" to and fro within the tank, or during driving on steep grades or parking on an incline, when fuel collects in a location away from the pump intake. Should the intake become uncovered, the pump will draw fuel vapor and air causing temporary interruption of fuel flow.
One approach to curtailing the "slosh" problem is to locate the pump intake, perhaps along with the pump itself, within a fuel accumulating reservoir in the fuel tank so that even when fuel level in the tank is low, a source of fuel is available to the fuel pump. During vehicle operation, the reservoir is filled with fuel, either by routing a portion of pressurized fuel to a jet pump to entrain fuel from the tank to the reservoir, as disclosed in U.S. Pat. No. 4,869,225 (Nagata et al.), or by routing return fuel to the fuel reservoir, as in U.S. Pat. No. 4,694,857 (Harris), or a combination of these, as disclosed in U.S. Pat. No. 5,070,849 (Rich, et al.) and U.S. Pat. No. 5,218,942 (Coha et al.), or other methods known to those skilled in the art and suggested by this disclosure.
A drawback of prior reservoir-based fuel delivery systems is time-induced efficiency decrease of the reservoir filling mechanism. For example, as the fuel pump ages, its efficiency typically decreases causing a decrease in delivery volume. If a portion of the fuel pump output is used as input to drive a jet pump for filling the reservoir, the jet pump delivery volume to the reservoir will also decrease. Since the fuel pump draws fuel directly from the reservoir, fuel pump demand may exceed jet pump output, resulting in the very problem sought to be solved in the first place, that is, insufficient fuel at the pump intake.
The just described problem may be exacerbated when pressurized, heated fuel from the fuel metering assembly is returned to the fuel reservoir whereupon it vaporizes causing a foam build-up therein. If drawn into the fuel pump, the foam may cause vapor lock and other concomitant problems.
An object of the present invention is to provide a fuel delivery system which ensures that sufficient liquid fuel is available at the fuel pump intake during low fuel level operation.
Another object is to provide a fuel delivery system which prevents vaporization of fuel returned to the fuel reservoir.
An advantage of the present invention is that the fuel pump draws fuel directly from the fuel tank, not the reservoir, until fuel within the tank falls below a predetermined level.
Another advantage is that a separate jet pump or similar device is not required to fill the reservoir.
Yet another advantage of the present invention is an enclosed fuel reservoir which accumulates fuel in a pressurized state so as to prevent vaporization and thus provide a source of liquid fuel to the fuel pump inlet when fuel in the tank falls below a predetermined level.
A feature of the present invention is an enclosed, pressurizable fuel reservoir which accumulates heated, pressurized fuel returned from the fuel metering system and retains the fuel in a liquid state by pressurizing same so as to prevent vaporization of the returned fuel.
Another feature is a reservoir overflow valve which allows fuel flow from the reservoir to the fuel tank when the reservoir is filled, the overflow valve being shut by a fuel level sender operatively associated therewith when fuel within the tank drops below a predetermined level so that pressure may build within the reservoir and open a valve leading to a conduit in fluid communication with the fuel pump inlet.